Recently, as demands for portable electronic products such as notebooks, video cameras, portable telephones and the like increase significantly, and development of medium or large size apparatuses such as electric vehicles, energy storage batteries, robots, satellites and the like is kicked into high gear, research on high performance secondary batteries that can be charged and discharged repeatedly is proceeding actively.
Currently, commercially available secondary batteries comprise nickel cadmium batteries, nickel hydrogen batteries, nickel zinc batteries, lithium secondary batteries, etc. Among them, lithium secondary batteries have drawn much attention because of little memory effect to allow unrestrained charging and discharging, as well as very low self-discharging rate and high energy density, compared to nickel-based secondary batteries.
Such secondary batteries are gathering attention as a new energy source for increasing environmentally friendliness and energy efficiency not only because of a primary advantage that they can innovatively reduce use of fossil fuels but also because they do not generate byproducts at all due to use of energy.
An energy storage system refers to a system configured to store electricity supplied from outside, and then to supply the stored electricity to the outside in case of emergencies such as blackouts. Such an energy storage system is basically comprised of a battery module and apparatuses that efficiently manage the battery module, and it is a concept that covers not only systems that store high-capacity electricity generated from power plants and the like but also apparatuses that store relatively low-capacity electricity such as portable electronic devices.
The battery module generally consists of an assembly consisting of a plurality of unit cells and a plurality of such assemblies, the unit cell including a positive electrode current collector, a separator, an active material, an electrolyte, an aluminum thin film layer and the like, and thus having a structure that is chargeable and dischargeable by an electrochemical reaction between configurative elements.
The life expectancy, stability and operational performance of the battery module depend on electrochemical or electrophysical characteristics of the unit cells included therein, wherein the electrochemical or electrophysical characteristics may change rapidly according to the external environment.
Especially, charging and discharging processes of the battery module are significantly influenced by the temperature of the battery module itself or its surrounding temperature. For example, when exposed to unfavorable conditions such as an extremely low temperature or an extremely high temperature, that is outside an optimum temperature range, the charging and discharging efficiency of the battery module decreases, and accordingly, a problem of difficulty in securing performance regarding a normal operation may occur. Further, the longer time the battery module is exposed to such unfavorable conditions, the more rapidly the life expectancy of the battery module decreases, and also, in some cases, there is a risk of explosion.
Conventional technologies measure the temperature of the space where the battery module is installed, and adjust the flow rate, temperature and the like of the cooling medium (e.g., air) being supplied to said space based on the measured temperature, so that the battery module can operate within a predetermined optimum temperature range. However, since a difference of temperature between the space where the battery module is installed and the battery module itself is inevitable, there are limitations in controlling the temperature exactly.
There are other conventional technologies as well, that receive temperature information of the battery module itself from a battery monitoring system (BMS) that is combined with the battery module, and control the temperature of the space where the battery module is installed based on the received temperature information. However, there is a problem that, when a situation occurs where communication with the BMS is impossible, temperature control of the battery module becomes impossible.